This invention relates to a method of making 3-hydroxy-2,4,5-trifluorobenzoic acid (HTBA) from an N-alkyl or N-aryl tetrafluorophthalimide. Specifically, a tetrafluorophthalimide is reacted with a base to produce a mixture of the salts of a 4-hydroxy-3,5,6-trifluoro N-substituted phthalamic acid (HTPA) and a 3-hydroxy-2,4,5-trifluoro N-substituted benzamide (HTB), the base is neutralized to form the HTPA and HTB, and the precipitate is acidified, which forms the HTBA.
U.S. Pat. No. 4,831,190, herein incorporated by reference, discloses a process for making HTBA by reacting tetrafluorophthalic acid with a base to form 4-hydroxy-3,5,6-trifluorophthalic acid, which is then decarboxylated. While that process is not known to be unsatisfactory, the starting material, tetrafluorophthalic acid, is considered to be too expensive for many applications.